<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>测试</title>
</head>
<body>

<script>
    var model = '<p><a target="_blank" href=""><img src="https://file.ceks100.com/group1/M00/00/E0/ctes31j5wNeAM46VAAq4p1q29mE333.png" alt="武汉理工大学智能医疗信息化研究中心授权@3x" style="max-width:100%;" class=""></a><br></p><p><br></p>';
    var t = model.substring(model.indexOf("http"),model.indexOf("><img") - 1);
    //console.log(t);

    var topAds;
    var topAdUrl = "";
    var topToExperts = "topToExperts";

    var checkWhickToLink = function () {
        var whickToLink = topAds == null?
            (topAdUrl.indexOf("http")==-1?topToExperts:topAdUrl):
            topAds;
        return whickToLink;
    };

    console.log(a = checkWhickToLink());
</script>

</body>
</html>